This invention relates generally to a position sensor, and more particularly, this invention relates to an improved and low-cost high resolution position sensor.
Position sensors with digital outputs provide discrete position information only whereas an analog position sensor can provide both position information and outputs that can be used to drive an electric motor or other similar electromechanical devices. Many of these devices are driven by sinusoidal excitations as a function of position. Consequently, an analog position sensor having an output that varies sinusoidally with position could be used to generate absolute angular positions as, for example, an electrical power steering system to measure the angle of rotation of the steering wheel, and/or reference signals to produce the desired sinusoidal phase drive currents and voltages to drive electric motors and other similar electro-mechanical devices.
Applications may further include throttle position sensors, pedal position sensors in drive-by-wire systems, body height position sensors for automotive suspension systems, etc.
The operational principle of an angle encoder sensor is based upon the property of Hall plates and semiconductor magnetoresistors, collectively referred to herein as magnetosensitive devices, to sense only the normal component of the magnetic field passing through them. Consequently, if a constant and uniform magnetic field is rotated in the plane perpendicular to the surface of a magnetosensitive device, the output signal will vary as the cosine of the angle between the direction of the incident magnetic field lines and the line normal to the surface of the device. Alternatively, Hall effect sensors may be usable when the magnetic field line changes in output and is not constant.
Prior motor shaft position sensors have utilized a series of high resolution and low resolution magnets arranged in a ring-shaped fashion, with a number of Hall sensors for both the high resolution and low resolution magnets. A back iron plate is also often used to hold the magnets. This arrangement may have limited resolution capability.